President Donald Trump said Saturday he would spare the European Union his steel and aluminum tariffs if the bloc halts its own trade barriers to US products, in his latest round of economic hardball.

The duties of 25 percent on imported steel and 10 percent on aluminum have stung the EU, along with other major partners including Japan, and European Trade Commissioner Cecilia Malmstroem said earlier Washington had failed to clarify how its allies could be spared.

"The European Union, wonderful countries who treat the U.S. very badly on trade, are complaining about the tariffs on Steel & Aluminum," Trump tweeted.

Malmstroem said negotiations would continue next week, after crunch talks with US Trade Representative Robert Lighthizer failed to defuse a bitter row that many fear could turn into an all-out trade war.

Brussels has gone the furthest in fighting back against Washington's shock measures, loudly announcing a list of US products to hit with countermeasures if its exports are affected by the tariffs.

Trump has said the tariffs, which will come into effect 15 days after he formally unveiled them Thursday, will not initially apply to Canada and Mexico. He also added Australia to the list of likely carve-outs.